1. Field of the Invention
The present invention relates to an imprint apparatus and an imprint method which are used for transferring a mold shape to a workpiece.
2. Description of the Related Art
In recent years, as described in “Stephan Y. Chou et. al., Appl. Phys. Lett, 67, 3114, 1995”, a fine processing technique for pressurizing and transferring a fine structure provided on a mold to a work such as a semiconductor, a glass, a resin, or a metal has been developed and attracted attention.
This technique is called nanoimprinting or nanoembossing because its resolution is on the order of several nanometers. According to this technique, a three-dimensional structure can be collectively processed at a wafer level at once. Therefore, thetechnique is expected to be applicable in a wide variety of fields in addition to manufacturing semiconductors.
For example, the technique is expected to be applied to manufacturing techniques for an optical device such as a photonic crystal, a micro total analysis system (μ-TAS), and a biochip.
An example will be described in which an optical imprint method is used for a semiconductor manufacturing technique.
First, a resin layer made of a photocurable resin is formed on a workpiece (for example, a semiconductor wafer).
Next, a mold on which a desirable depressed and projected structure is formed is pressed against the resin layer and pressurized thereagainst.
The resin layer is irradiated with ultraviolet light to cure the photocurable resin, thereby transferring the structure to the resin layer. Etching is performed using the resin layer as a mask, so that the structure is transferred to the workpiece.
In such semiconductor manufacturing process, it is necessary to align the mold and the workpiece.
For example, in the current circumstances in which a semiconductor process rule is 100 nm or less, it is said that an allowable range of an alignment error attributable to an apparatus is several nm to several tens nm.
A method of aligning a mold with a workpiece based on the fact that the focus length is changed according to the wavelength of light is disclosed in U.S. Pat. No. 6,696,220. To be specific, a mark provided on the surface of a mold is imaged to an image pick-up device at a first wavelength and a mark on the surface of a workpiece is imaged to the image pick-up device at a second wavelength different from the first wavelength. The two wavelengths are selected according to a gap formed between the mold and the workpiece.
In the case of the first wavelength, although focus is achieved on the mark provided on the surface of the mold, focus is not achieved on the mark provided on the surface of the workpiece. In contrast to this, in the case of the second wavelength, although focus is not achieved on the mark provided on the surface of the mold, focus is achieved on the mark provided on the surface of the workpiece.
An image of the mark provided on the surface of the workpiece, on which focus is not achieved at the first wavelength, is measured. Similarly, an image of the mark provided on the surface of the mold, on which focus is not achieved at the second wavelength, is measured. The measured images are removed by image processing. After that, an image of the mark provided on the surface of the mold, on which focus is achieved at the first wavelength, is measured. Similarly, an image of the mark provided on the surface of the workpiece, on which focus is achieved at the second wavelength, is measured. The measured images are combined with each other on a single imaging plane.
A method of aligning a mask with a wafer in a semiconductor exposure apparatus is further disclosed in U.S. Pat. No. 6,529,625.
To be specific, when the relative position between the mask serving as a first object and the wafer serving as a second object is to be detected, a third object on which a reference alignment mark different from marks for determining positions on the respective objects is located is provided. An optical image of the mark located on the third object and optical images of the marks located on the first and second objects are detected by an image pick-up device to detect position shifts of the first and second objects. In the apparatus, an image pick-up device for imaging the mark located on the first object is different from an image pick-up device for imaging the mark located on the second object and a part of optical systems thereof is commonly used.
The prior art method of aligning the mold with the workpiece as described in U.S. Pat. No. 6,696,220 employs a structure in which different light sources are used to utilize light beams having different wavelengths. Therefore, when the mold and the workpiece are continuously changed in a direction perpendicular to a working surface, it is difficult to align the mold and the workpiece.
On the other hand, the prior art method of aligning the mask with the wafer as disclosed in U.S. Pat. No. 6,529,625 is useful in the case where the alignment is performed with a specific gap, such as the case using a light exposure machine.
However, in the case of a nanoimprint apparatus, the distance between a mold and a workpiece which are opposed to each other continuously changes, so it is required to align the mold and the workpiece with respect to an arbitrary gap.
Such a requirement occurs, for example, when a resin is interposed between the mold and the workpiece. That is, before and after the mold becomes in contact with the resin or when pressurization is performed in a state in which the resin is applied, a position shift between the mold and the workpiece easily occurs.
When the position shift is large, the alignment takes a long time.
Therefore, when the distance between the mold and the workpiece is to be continuously changed, a structure capable of performing high-precision alignment in a short time is required.